Latitudinal variation and driving factors of above-ground carbon proportion of large trees in old-growth forests across China

Large trees play a vital role in forest carbon stocks, dominating the distribution of community biomass. However, climate change and deforestation are reducing large trees globally, resulting in regional differences in their contribution to carbon stocks. Here, we examined the latitudinal change pattern and drivers of large trees' contributions to stand carbon stocks. Above-ground carbon storage was calculated for 530 plots in old-growth forests across China. Linear regression was used to calculate latitudinal variation in the proportion of above-ground carbon in large trees (i.e., AGC proportion). Variance partitioning and multiple linear regression were used to calculate the relative importance of species diversity, stand structure, functional traits, and environmental factors to AGC proportion. The study found that AGC proportion decreased with increasing latitude, averaging at 64.44 %. Stand structure, particularly the coefficient of variation of DBH, was identified as the key drivers of the AGC proportion. The number of common species (Hill's 1D) had no direct effect on the AGC proportion, while wood density, maximum tree height, and leaf nitrogen-to‑phosphorus ratio showed negative effects. The mass-ratio effects on AGC proportion were stronger than diversity effects. Climate variables primarily affected the AGC proportion through stand variables. These results indicate that simultaneously managing high diversity and AGC proportion may pose challenges. Moreover, considering the substantial contribution of large trees to carbon stocks, their storage capacity and sensitivity to environmental changes exert significant control over forest carbon cycles. Therefore, preserving and enhancing the carbon sink function of old-growth forests in the face of climate change and disturbance may depend primarily on protecting existing large trees and soon-to-be large-diameter trees.

Profile of tree-related microhabitats in the primeval Białowieża Forest: A benchmark for temperate woodlands

Tree-related Microhabitats (TreMs) are a key structural element having a significant impact on the biodiversity and functioning of forest ecosystems. Although forests enjoying long-term protection host richer and more abundant TreMs compared to managed stands, the quantity and quality of such microstructures in primeval temperate forests are unknown. This study investigates for the first time the assemblage of TreMs in the Białowieża Forest (BF), which is regarded as the last surviving fragment of pristine lowland forests in the temperate zone of Europe. Relatively undisturbed by human activity since the last glacial period, the BF ecosystem has remained remarkably intact, which may have given rise to its unique TreM assemblage. Here, we show that a primeval forest is characterized by an exceptionally high richness and density of TreMs compared to previously studied natural forests, and that the richness, density and diversity of TreMs are spatially heterogeneous at the micro-scale but homogeneous at the macro-scale. This indicates that adjacent small fragments of habitat (0.05 ha) may have different TreM profiles, but large patches of forest (several ha) host similar assemblages of TreMs. Our profile of TreMs depends on the basal area and density of living trees, the basal area of dead standing trees and the dominance of specific TreM-hosting tree species in a stand. Our study suggests that both the ecological continuity and complexity of a forest supporting many different tree species and the diversity of TreM-forming biota that typically occurs in primeval temperate forests are factors that appear to contribute to the observed profile of TreMs. The results of our study set a benchmark for the quantity and quality of TreMs in broadleaved temperate forests and indicate that the long-term spontaneous natural processes occurring in primeval forests lead to the emergence of ultra-rich, complex assemblages of TreMs.

COVID-19 shutdown revealed higher acoustic diversity and vocal activity of flagship birds in old-growth than in production forests

The COVID-19 shutdown has caused a quasi-experimental situation for ecologists in Spring 2020, providing an unprecedented release in acoustic space for avian soundscapes due to the lowest technophony levels experienced for decades. We conducted large-scale passive acoustic monitoring in 68 forest stands during and after the shutdown to compare their acoustic diversity under different management regimes. We designed a before-after sampling scheme of 18 paired stands to evaluate the short-term effect of shutdown on diel and nocturnal acoustic diversity of forest soundscapes. We assessed whether old-growth preserves hosted higher acoustic diversity and vocal activity of flagship specialist birds than production stands during the shutdown, and whether the effect of management was mediated by landscape fragmentation and distance to roads. We derived acoustic richness and vocal activity of flagship specialist birds by systematically performing 15-min long aural listening to identify species vocalizations from all recorded stands. The end of the COVID-19 shutdown led to a rapid decrease in diel and nocturnal biophony and acoustic diversity. During the shutdown, we found significantly higher biophony and acoustic diversity in old-growth preserves than in production stands. Bird acoustic richness and vocalizations of the two most frequent flagship specialists, Dendrocoptes medius and Phylloscopus sibilatrix, were also both higher in old-growth stands. Interestingly, this positive effect of old-growth stands on forest soundscapes suggested that they could potentially attenuate traffic noise, because the distance to roads decreased acoustic diversity and biophony only outside old-growth preserves. Similarly, flagship bird richness increased with old-growth cover in the surrounding landscape while edge density had a negative effect on both acoustic diversity and flagship birds. We suggest that enhancing the old-growth preserve network implemented across French public forests would provide a connected frame of acoustic sanctuaries mitigating the ever-increasing effect of technophony on the acoustic diversity of temperate forest soundscapes.

Tree microhabitats in natural temperate riparian forests: An ultra-rich biological complex in a globally vanishing habitat

Tree-related microhabitats (TreMs) are among the most important structural components of a forest, and have a significant impact on biodiversity and influence ecosystem functioning. Although forests that depend on natural lowland water regimes are severely endangered worldwide, and floodplain forests are considered to be the most complex and biologically rich habitats in the temperate zone, the TreMs in them have yet to be identified. This study investigates the assemblage of TreMs in natural Willow-Poplar riparian forests and analyses the environmental factors that influence their qualitative and quantitative compositions. A total of 90 sample plots (0.05 ha each) were selected at random in old-growth riparian forests that occur along a large unregulated river, the Vistula (Poland). A total of 62 TreM types were identified with a mean number of 16.0 ± 4.6 SD TreM types per plot and a mean density of 829.4 ± 360.1 SD TreM-bearing trees ha^-1. The number of TreMs found on an individual tree depends on its diameter, the number of trunks, its living status (living vs. dead tree) and the species it belongs to. The richness, density and diversity of TreMs found on a plot depends on the density of living trees, the basal area of living or dead trees, the number of tree species, and the percentage of Willows Salix sp. or of multi-trunk trees. Our study records for the first time the assemblage of TreMs in natural Willow-Poplar riparian forests and provides a reference for floodplain habitats. The results indicate that multi-species forests influenced by natural waterflow-related disturbances are hot-spots of TreM richness and abundance, and highlight the urgent need for the protection or restoration of these vanishing habitats.

Long term effects of fire on the soil greenhouse gas balance of an old-growth temperate rainforest

Forest fires can cause great changes in the composition, structure and functioning of forest ecosystems. We studied the effects of a fire that occurred >50 years ago in a temperate rainforest that caused flooding conditions in a Placic Andosol to evaluate how long these effects last; we hypothesized that the effects of fire on the soil greenhouse gas (GHG) balance could last for many years. We made monthly measurements of fluxes of carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) during two years of soils in an unburned forest (UF) and a nearby site that burned >50 years ago (BS). Our results show that CO₂ emissions from soils were higher in the UF than in the BS, and positively correlated with temperature and negatively with soil water content at both sites. Both sites were net CH₄ sinks (higher in the UF) and fluxes correlated positively with soil water content and negatively with temperature (stronger relation in the BS). Emissions of N₂O were low at both sites and showed correlation with friction velocity at the UF site. The soil GHG balance showed that the UF emitted about 80% more than the BS (5079 ± 1772 and 2815 ± 1447 g CO₂-eq m^-2 y^-1, respectively). Combining our measured fluxes with data of CO₂ net ecosystem exchange, we estimated that at the ecosystem level, the UF was a GHG sink while the BS was a source, showing a long-lasting effect of the fire and the importance of preserving these forest ecosystems.

Long-term population persistence of flightless weevils (Eurhoptus pyriformis) across old- and second-growth forests patches in southern Appalachia

Background

Southern Appalachian forests are dominated by second-growth vegetation following decades of intensive forestry and agricultural use, although some old-growth patches remain. While it’s been shown that second-growth areas may exhibit comparable species richness to old-growth in the area, the extent to which populations of arthropods in second-growth areas have persisted vs. recolonized from other areas remains unexamined. The implications for conservation of both classes of forest are significant. Here we analyze population diversity and relatedness across five old-growth and five second-growth populations of flightless, leaf litter-inhabiting beetles in the genus Eurhoptus (Coleoptera: Curculionidae: Cryptorhynchinae). Our main goal is asking whether second-growth areas show diminished diversity and/or signals of recolonization from old-growth sources.

Results

Population genetic and phylogenetic analyses do not reveal any consistent differences in diversity between the old-growth and second-growth populations examined. Some second-growth populations retain substantial genetic diversity, while some old-growth populations appear relatively depauperate. There is no phylogenetic indication that second-growth populations have recolonized from old-growth source populations.

Conclusions

Most populations contain substantial and unique genetic diversity indicating long-term persistence in the majority of sites. The results support substantial resilience in second-growth populations, though the geographic scale of sampling may have hindered detection of recolonization patterns. Broad scale phylogeographic patterns reveal a deep break across the French Broad River basin, as has been reported in several other taxa of limited dispersal abilities. In Eurhoptus this break dates to ~ 2–6 Ma ago, on the older end of the range of previously estimated dates.

Electronic supplementary material

The online version of this article (10.1186/s12862-018-1278-y) contains supplementary material, which is available to authorized users.

Exploring indigenous landscape classification across different dimensions: a case study from the Bolivian Amazon

Decisions on landscape management are often dictated by government officials based on their own understandings of how landscape should be used and managed, but rarely considering local peoples' understandings of the landscape they inhabit. We use data collected through free listings, field transects, and interviews to describe how an Amazonian group of hunter-horticulturalists, the Tsimane', classify and perceive the importance of different elements of the landscape across the ecological, socioeconomic, and spiritual dimensions. The Tsimane' recognize nine folk ecotopes (i.e., culturally-recognized landscape units) and use a variety of criteria (including geomorphological features and landscape uses) to differentiate ecotopes from one another. The Tsimane' rank different folk ecotopes in accordance with their perceived ecological, socioeconomic, and spiritual importance. Understanding how local people perceive their landscape contributes towards a landscape management planning paradigm that acknowledges the continuing contributions to management of landscape inhabitants, as well as their cultural and land use rights.

Multi-decade biomass dynamics in an old-growth hemlock-northern hardwood forest, Michigan, USA

Trends in living aboveground biomass and inputs to the pool of coarse woody debris (CWD) in an undisturbed, old-growth hemlock-northern hardwood forest in northern MI were estimated from multi-decade observations of permanent plots. Growth and demographic data from seven plot censuses over 47 years (1962–2009), combined with one-time measurement of CWD pools, help assess biomass/carbon status of this landscape. Are trends consistent with traditional notions of late-successional forests as equilibrial ecosystems? Specifically, do biomass pools and CWD inputs show consistent long-term trends and relationships, and can living and dead biomass pools and trends be related to forest composition and history? Aboveground living biomass densities, estimated using standard allometric relationships, range from 360–450 Mg/ha among sampled stands and types; these values are among the highest recorded for northeastern North American forests. Biomass densities showed significant decade-scale variation, but no consistent trends over the full study period (one stand, originating following an 1830 fire, showed an aggrading trend during the first 25 years of the study). Even though total above-ground biomass pools are neither increasing nor decreasing, they have been increasingly dominated, over the full study period, by very large (>70 cm dbh) stems and by the most shade-tolerant species (Acer saccharum and Tsuga canadensis).

CWD pools measured in 2007 averaged 151 m³/ha, with highest values in Acer-dominated stands. Snag densities averaged 27/ha, but varied nearly ten-fold with canopy composition (highest in Tsuga-dominated stands, lowest in Acer-dominated); snags constituted 10–50% of CWD biomass. Annualized CWD inputs from tree mortality over the full study period averaged 1.9–3.2 Mg/ha/yr, depending on stand and species composition. CWD input rates tended to increase over the course of the study. Input rates may be expected to increase over longer-term observations because, (a) living biomass is increasingly dominated by very large trees whose dead trunks have longer residence time in the CWD pool, and (b) infrequent major disturbances, thought to be important in the dynamics of these forests, have not occurred during the study period but would be expected to produce major, episodic pulses in CWD input.

Few fragments of old-growth cool-temperate forests remain, but such forests can constitute a very large carbon pool on a per-area basis. The carbon sink/source status of these forests remains unclear. While aboveground living biomass at this study site shows no strong aggrading or declining trend over the last half-century, this remains a modest span in the innate time-scale of late-successional forest. The effects of rare disturbances, long-term shifts in composition and size structure, and changes in soil carbon and CWD pools may all influence long-term carbon status.